Ranalisma rostratum (Alismataceae) is an endangered aquatic plant, and now there is only one population existing in China. In its natural habitat, Huli marsh in Chaling, Hunan province, the best growing plants have be...Ranalisma rostratum (Alismataceae) is an endangered aquatic plant, and now there is only one population existing in China. In its natural habitat, Huli marsh in Chaling, Hunan province, the best growing plants have been observed at microsites where the water depth is 5～10cm, and the plants grow in emergent form.R. rostratum reproduces asexually or sexually. The recruitment of asexual propagules into population is a very important way to maintain the natural population size. Although seed production does not appear to limitR. rostratum, restricted dispersal of propagules and seeds, low seed viability, low germinability, slow growth of seedlings under all conditions, and habitat loss due to agriculture appear to be more important reasons for the endangerment of this plant.展开更多
The nonthermal components in hard X-rays have been detected in two young supernova remnants （SNRs）： SN 1006 and Kepler＇s SNR. Various theoretical models showed that the amplification of the magnetic field was cruc...The nonthermal components in hard X-rays have been detected in two young supernova remnants （SNRs）： SN 1006 and Kepler＇s SNR. Various theoretical models showed that the amplification of the magnetic field was crucial to explain their multiband emission properties. We investigate the evolution of the magnetic field and model the multiband emissions from these two young SNRs with a time-dependent injection model. The results indicate that （1） the radio and X-ray emissions are re- produced by synchrotron radiation of the injected electrons, while the y-rays can be explained as inverse Compton scattering of the relativistic electrons and proton-proton interaction of the high-energy protons; and （2） the amplification of the magnetic field spontaneously happens with reasonable parameters.展开更多
文摘Ranalisma rostratum (Alismataceae) is an endangered aquatic plant, and now there is only one population existing in China. In its natural habitat, Huli marsh in Chaling, Hunan province, the best growing plants have been observed at microsites where the water depth is 5～10cm, and the plants grow in emergent form.R. rostratum reproduces asexually or sexually. The recruitment of asexual propagules into population is a very important way to maintain the natural population size. Although seed production does not appear to limitR. rostratum, restricted dispersal of propagules and seeds, low seed viability, low germinability, slow growth of seedlings under all conditions, and habitat loss due to agriculture appear to be more important reasons for the endangerment of this plant.
基金supported by the National Natural Science Foundation of China(Grant No.11173020)the National Basic Research Program of China(973Program,2009CB824800)
文摘The nonthermal components in hard X-rays have been detected in two young supernova remnants （SNRs）： SN 1006 and Kepler＇s SNR. Various theoretical models showed that the amplification of the magnetic field was crucial to explain their multiband emission properties. We investigate the evolution of the magnetic field and model the multiband emissions from these two young SNRs with a time-dependent injection model. The results indicate that （1） the radio and X-ray emissions are re- produced by synchrotron radiation of the injected electrons, while the y-rays can be explained as inverse Compton scattering of the relativistic electrons and proton-proton interaction of the high-energy protons; and （2） the amplification of the magnetic field spontaneously happens with reasonable parameters.
